For Future Reference

To get dual-head output on a recent Intel integrated graphics card, such as the 965 GM inside my Lenovo T-61 laptop, when running Fedora 10, only one relatively non-intuitive step is needed. The virtual desktop size must first be increased inside xorg.conf so that both screens can fit inside the single X framebuffer:

Section "Screen"
   SubSection "Display"
      Virtual 3072 1680

Once this is done, you can plug in a display (say, a projector), go to the “Resolution” preferences applet, and enable the new display at a reasonable resolution. F10’s version of even has a fancy two-screen presentation mode that shows a countdown timer, the next slide, etc.

Answer discovered on this documentation page.